1. Field of the Invention
The present invention is directed to a process for removing residual slurry after chemical mechanical polishing employing a supercritical fluid. More specifically, the present invention is directed to a process for removing residual slurry arising from planarizing of workpieces by utilizing composition of a supercritical fluid, which includes supercritical carbon dioxide and a co-solvent, and a surfactant.
2. Background of the Prior Art
A common and well established method of planarizing semiconductor wafers and other workpieces is by polishing surfaces to be planarized with a chemical mechanical polishing (CMP) slurry. Those skilled in the art are aware that these slurries are silica-based, tungsten-based, ceria-based or alumina-based and are used to remove silicon, metal coatings, silicon oxides and silicon nitrides and the like on silicon. As a result of this polishing, residual slurry, combined with the removed material, becomes deposited on all exposed areas of the workpiece.
In the past conventional brush and wet cleaning of residual CMP slurry was utilized. However, in view of the continuing decreased size of semiconductor devices, this brush and wet cleaning method, which utilizes water, has been less and less successful. This is so because water and other aqueous fluids employed in wet cleaning techniques have relatively high surface tensions. Water, for example, has a surface tension of about 70 dynes per square centimeter. This relatively high surface tension makes it very difficult or even impossible to dislodge and remove debris from vias, trenches and other nanostructures.
This difficulty is scientifically explained by the force of particle adhesion to a substrate surface. This adhesive force is dependent upon the adhesion between the debris particle and the surface. The major adhesive forces, which hold the debris to the surface, are Van der Waals and electrostatic forces. The semiconductor devices of the present day and even more so in the future have and will have substructures in the order of submicron dimensions. To remove residual CMP slurry particles left after chemical mechanical polishing, requires a low surface tension fluid that is able to penetrate into a depression and into the interface between a debris particle and the surface in which the particle is entrapped inside a submicron depression. Thus, it is apparent that a totally new process must be devised to ensure that debris particles, resulting from chemical mechanical polishing, are removed.
Recent developments have focused on removal of residues from semiconductor surfaces, albeit not necessarily CMP slurry residues. U.S. Pat. Nos. 5,908,510 and 5,976,264 involve the removal of residue from an etched precision surface utilizing supercritical fluids or liquid carbon dioxide. More specifically, the residue removed from etched precision surfaces in these disclosures are fluorine- or chlorine-containing residues. These disclosures also indicate that a cryogenic aerosol, which may be argon, nitrogen or carbon dioxide, may be employed as a subsequent step after processing with a supercritical fluid or liquid carbon dioxide.
U.S. Pat. No. 5,306,350 describes a method of cleaning apparatus by removing one or more polymeric compounds therefrom. This is accomplished by a cleaning composition which includes at least one compressed fluid, which is a gas at standard conditions, and a solvent. The at least one or more removed polymeric compounds are at least partially soluble in the solvent and at least partially miscible with the compressed fluid. This compressed fluid may be supercritical carbon dioxide, nitrous oxide or a mixture thereof. This method is preferably accomplished by spraying.
European Patent Application 0 572 913 describes a system of continuously processing items using a supercritical fluid in which the items to be cleaned or extracted are continuously pressurized with the supercritical fluid.
European Patent Application 0 726 099 is directed to a process of removing surface contaminants from a substrate by contacting the substrate with a dense phase gas at or above the critical pressure thereof. A preferred dense phase gas is carbon dioxide.
Although the aforementioned references represent advances in the art, none of them address the specific problem of removing chemical mechanical polishing slurry residue from semiconductor surfaces and nanostructures. Thus, there is a continuing need in the art for a new process to address this important problem.
A new process has now been developed for removal of residual chemical mechanical polishing (CMP) slurry from topographical structures on semiconductor wafers. This residual CMP slurry removal eliminates problems in subsequent processing operations which lead to contamination, electrical device opens, electrical device shorts and other yield/reliability concerns.
Although the invention is not limited to any theory explaining its operation, it is believed that two requirements must be met in order to overcome the difficulties discussed above. First, a residual slurry removal fluid must be utilized which has a low enough surface tension to permit the fluid to penetrate into very narrow openings. Secondly, the fluid must be able to neutralize any charge on the slurry particles to allow the fluid to not only penetrate into the narrow openings but also dislodge the residual slurry particles. The invention of the present application provides a cleaning fluid which meets these physical requirements.
In accordance with the present invention a process is provided for removal of residual slurry resulting from chemical mechanical processing which comprises removing residual slurry resulting from chemical mechanical polishing with a composition which comprises a mixture of a supercritical fluid, wherein the supercritical fluid comprises carbon dioxide and a co-solvent and a surfactant.